Internal combustion engines such as those used in the automotive industry typically have one or more camshafts which open and close intake and exhaust valves for passing air and exhaust gasses to and from one or more combustion chambers. A rotary shaft is connected to displacement members such as pistons or rotors which are moveably disposed for determining the volume of corresponding combustion chambers. Timing belts and timing chains have been used for connecting rotary shafts to respective camshafts to provide cam timing so that the intake and exhaust valves will be opened and closed in cooperative relation with displacement members moving within combustion chambers.
Application of electronics to modern internal combustion engines has resulted in electronic control of engine functions, from electronic ignition timing, to throttle control and fuel injection. Timing belts and timing chains in some prior art engines have been replaced by stepper motors controlling cam timing for opening and closing conventional intake and exhaust valves. In some prior art piston engines energy is conserved by skipping operation of predetermined cylinders when engine power requirements are low, and then all cylinders may be used when engine power requirements are high. Fuel will not be injected into cylinders when not being used. This has caused harmful engine deposits to buildup when the same preselected cylinders are continuously not used in lower power modes and are especially troublesome for conventional valves. For skipped cylinder combustion engines in which carburetors are used, emissions are increased since fuel that would normally be burned during combustion is now emitted to the atmosphere as a gas when a particular cylinder is skipped.